There are many microorganisms that have a useful enzymatic activity, and such microorganisms are widely used in the production of functional food materials such as carbohydrates, amino acids, and phospholipids. Among these, there are known many microorganisms which can be used in the production of carbohydrate materials, particularly oligosaccharides, and for example, it has been reported that a galactooligosaccharide is produced by utilizing the β-galactosidase activity of yeast belonging to the genus Sporobolomyces singularis (PTL 1). It has also been reported that a mutant microorganism in which the β-galactosidase activity of Sporobolomyces singularis has been increased was created (PTL 2).
It is, however, difficult in terms of technology and cost to industrially release and purify the above-described β-galactosidase of Sporobolomyces singularis since the enzyme is tightly bound to the cell walls of the microorganism, like some other enzymes produced by microorganisms. Therefore, when β-galactosidase of Sporobolomyces singularis is industrially utilized, it is supplied in the form of a dilute microbial cell liquid, however, utilization form poses a problem.
Namely, the utilization form has the following problems: the storage and distribution costs are too expensive because the dilute microbial cell liquid has such form that it contains water, a buffer, etc. in an amount several times more than the amount of the microbial cells; it is difficult to control microbial contamination because of the liquid form and such form is not suitable for a long-term storage; and in order to decrease the risk of microbial contamination, it is necessary to produce the product on a demand-led basis.
In particular, it is essential to come up with a solution to the above-given problems in order to produce industrially a galactooligosaccharide at low cost using β-galactosidase of Sporobolomyces singularis, and the development of a means of maintaining the enzymatic activity of a microorganism even in a dry state has been desired.